Deep resistivity cross section of the intraplate Atlas Mountains (NW Africa): New evidence of anomalous mantle and related Quaternary volcanism

Abstract

[1] The Atlas Mountains are characterized by high elevations and Quaternary volcanism. Long period magnetotelluric data acquired along a NNW-SSE transect reveal the presence of a conductive anomalous mantle below the High Atlas. Data dimensionality analyses show a preferent N80°E strike of the deep resistivity structure in agreement with the induction vector alignment at long periods. Accordingly, a 2D inversion of the data set was carried out. Large resistive bodies at the crustal basement most likely correspond to batholiths emplaced in more conductive metapelites. They are covered by outcropping conductive sedimentary detritic and carbonate rocks. Lithospheric thinning producing anomalous mantle and basin development in the Atlas probably started during Triassic-Jurassic rifting. Inversion tectonics since the Oligocene produced low shortening on previous lithospheric weak zones, with thrusting of the Atlas above the stable African plate. Melting at the top of the anomalous mantle is connected with Quaternary basaltic volcanism in the Middle Atlas.

Comment on “Deep resistivity cross section of the intraplate Atlas Mountains (NW Africa): New evidence of anomalous mantle and related Quaternary volcanism”

“…However, the data and resulting model on which their interpretation is based are highly suspect, particularly at the longer periods pertaining to lithospheric mantle depths, meaning that the corresponding interpretation has not been proven by the extant data and cannot be trusted. We have little issue with the crustal part of Anahnah et al 's [2011] model; we contend that the mantle part of their model is highly suspect and that the evidence for thinned lithosphere is simply nonexistent in their data, and indeed is refuted by their data, but appears to be contrived to fit preconceived notions. Our views are entirely based and stated on objective criteria, and suggestions otherwise are refuted and are attempts to detract from our criticisms.…”

“…The data acquired by Anahnah et al [2011] are exemplified in their paper by MT response plots (apparent resistivity and phase curves) of only four of the 19 sites acquired of useful data (of the 21 total sites, sites 08 and 10 are listed as “no available” (sic) in the phase tensor plot in Anahnah et al 's [2011] Figure 3) in Anahnah et al 's [2011] Figure 4. Those selected four, we have to presume, are representative.…”

“…In their paper, modeling magnetotelluric (MT) data across the Atlas Mountains, Anahnah et al [2011] undertake a tectonic interpretation of a derived electrical resistivity model focusing particularly on a region of purported anomalously low resistivity in the uppermost mantle. However, the data and resulting model on which their interpretation is based are highly suspect, particularly at the longer periods pertaining to lithospheric mantle depths, meaning that the corresponding interpretation has not been proven by the extant data and cannot be trusted.…”

“…At issue is that the data used to construct the two‐dimensional (2D) model presented by Anahnah et al [2011, Figure 4] are questionable, the adopted strike direction is likely invalid, the model does not meet the dimensionality of the data, the model does not fit the data adequately, and the model was not subsequently appraised sufficiently for resolution. 2D modeling is appropriate at those periods sampling the crust, and is also reasonably appropriate for those periods sampling the mantle, but as the crust and mantle have different geoelectric strike directions, 2D modeling of the whole bandwidth of crustal and mantle periods is not appropriate.…”

New numerical and theoretical model to characterize the upper crustal structure of the Moroccan atlas from wide-angle seismic reflection data

“…All these uncommon features make this orogen very attractive for diverse studies, like field investigations mostly of structural geology since 1976 by Michard [10], and later by other authors [4], [5], gravimetric crustal model calculation [7], [9], [11], teleseismic P wave tomography [12], magnetotelluric investigations [1], [13], [14] low-resolution seismic refraction profile [8], [15], receiver functions analysis [16], [17], GPS measurements [18] and potential fieldbased lithospheric model [19]. Yet the Atlas Mountains are still the subject of ongoing research in an effort to constrain the deep structure in which most models have their basis [20] but also the velocity structure of its upper subsurface.…”